Cold Spring Harbor Laboratory Conference on Telomeres and Telomerase May 4-8, 2005. Telomeres are specialized protein-DNA complexes that protect the ends of eukaryotic chromosomes. In most eukaryotes, telomeres contain short DNA repeats that are maintained by the telomerase reverse transcriptase. Since telomerase counteracts the terminal sequence loss that accompanies replication of linear DNA, the enzyme is required for long term cellular proliferation. The field of telomere biology has grown rapidly since it was recognized that telomere dynamics and telomerase activation play a pivotal role in human cancer and in cellular senescence. As a result, the telomere field is now a highly diverse and dynamic area, representing a wide variety of research interests (cancer, aging, cell cycle, meiosis, recombination, replication, etc.) and a large number of different model organisms (mammals, fungi, protozoa, plants). The previous three Cold Spring Harbor Laboratory meetings on Telomeres and Telomerase, were crucial in bringing together this diverse group of researchers and resulted in vigorous discussion and synergistic interactions stimulated by the presentation of a very large body of unpublished data. Since the CSH Telomere and Telomerase meeting represents the only opportunity for scientists in this rapidly growing field to interact as a whole, this meeting is of the utmost importance for the future of the field. Furthermore, the format of CSH meetings, where all talks are chosen from submitted abstracts, maximizes the opportunity for new researchers and young investigators to present their most recent unpublished work. The prior meetings had a uniformly high attendance rate from an international group of researchers. The platform presentations and posters at the past meeting presented the major discoveries in the field well before publication. We anticipate that the 2005 meeting will be equally well attended. The subsequent meetings (2007 and 2009) will follow a similar format and will include topics that are highly relevant at the time of the meeting.